*6.4.1 Phenotypic assays*

The WHO bioassays have been conducted in many species of Triatominae against DDT resistance [94], where behavioral responses were observed in *T. infestans* strains to deltamethrin, on the basis of which the insect populations were differentiated into susceptible and resistant [95]. The other behavioral and environmental factors such as dispersal or migration of the vector populations leading to the changes in feeding behavior, nutritional status and reproductive behavior also contribute to the alterations in the response to insecticides [96]. Therefore, observation of such changes can be utilized in detection of insecticide resistance in vector populations.
